A prefabricated wall panel is known having the core of insulating material sandwiched between two substantially parallel facing sheets. Along one side edge of the wall panel the facing sheets extend beyond the core of material and form free edges. On the opposite side edge there is provided a connecting element having two tongues extending outwardly of the panel toward an adjacent panel with one of the facing sheets extending around each of the two outer tongue portions of the two outer tongues. A connecting segment extends between the two tongues.
As conventionally designed such a wall panel when joined to an adjacent wall panel generally has an interior space having only a very small insulating capability, or none at all at the joint between the connecting member on the edge of one panel and the edge of the core of the complimentary opposite edge of an identical adjacent panel. Accordingly, heat transmission in either direction through the joint is readily possible between the free edges of the facing sheets since the joint has such a poor insulating capability. Frequently, as well, this joint structure lacks strength often to the point of being insufficient for the purpose.